The Vi headphones have a couple different sensors, including a touch sensor (for interacting with Vi), a gyroscope (for rotational motion), accelerometer (for movement or vibrations) and a barometer (for elevation / atmospheric pressure). Plus they house a “custom” sensor that uses visible-light and infrared LEDs along with photodiodes, all in the left ear bud, to determine your heart rate. The headphones can also talk to your iPhone/Android's GPS and Wi-Fi to help with figuring out location and other information.